Data are presented showing that a quantum-dot (QD)heterostructurediode, with an auxiliary ∼20 Å InGaP quantum well(QW) coupled via an In(AlGa)P barrier (∼20 Å) to the single layer of QDs to aid carrier collection, has a steeper current–voltage characteristic than the case of a similar diode with no auxiliary QW. The diode is capable of 300 K visible-spectrum QDlaser operation, while the single-layer InP QDdiode (single QD layer) saturates at low current (≲1 mA) and does not exhibit stimulated emission.

Absorption spectra obtained from spark-processed Si (sp-Si) utilizing differential reflectometry yield a series of closely spaced energy levels, as expected for amorphous materials, which reside between 1.7 and 2.8 eV. Further, a broad absorption band is observed between about 3.2 and about 6.2 eV. A HeCd laser pumps electrons from the ground state into this absorption band. The blue and green photoluminescence peaks of sp-Si are interpreted as originating from emission energy levels at 3.22 and 2.36 eV into which the electrons revert from the just mentioned absorption band by nonradiative transitions. In contrast, pumping with an argon ion laser provides only enough energy to excite the electrons from the ground state into the above mentioned, closely spaced, lower absorption bands and thus causes only a 1.9 eV (red) radiation.

We report a photonic-crystal distributed-feedback (PCDFB) laser with an antimonide type-II “W” active region. Optical lithography and dry etching were used to pattern the two-dimensional rectangular lattice with a second-order grating tilted by 20° relative to the facet normal. For pulsed optical pumping, the emission line centered on is considerably narrower (7–10 nm) than for Fabry-Pérot and angled-grating DFB (α-DFB) lasers fabricated from the same wafer. The PCDFB beam quality is also substantially enhanced, e.g., by a factor of 5 compared with the α-DFB at a pump-stripe width of 200 μm.

By using a perturbative approach, we propose a simple, systematic, and efficient method to engineer acoustic band gaps. A gap can be enlarged or reduced by altering the microstructure according to the field-energy distributions of the Bloch states at the band edges as well as their derivatives. Due to the structure of the acoustic waveequation, the engineering of acoustic band gaps is much more efficient than that of photonic band gaps. The validity of the proposed method is supported by multiple-scattering calculations. Our method makes the acoustic band gap “designable.”

An angle-dependent surface photovoltage spectroscopy (SPS) study has been performed at room temperature on a GaAs/GaAlAs-based vertical-cavity-surface-emitting-laser (VCSEL) structure emitting at a wavelength near 850 nm. For comparison purposes, we have also measured the angle-dependent reflectance (R). The surface photovoltage spectra exhibit both the fundamental conduction to heavy-hole (1C–1H) excitonic transition and cavity mode plus additional interference features related to the properties of the mirror stacks, whereas in the Rspectra only the cavity mode and interference features are clearly visible. The energy position of the excitonic feature is not dependent on the angle of incidence, in contrast to that of the cavity mode, whose angular dependence can be fitted with a simple model. This study demonstrates the considerable potential of angle-dependent SPS for the contactless and nondestructive characterization of VCSEL structures at room temperature.

The strain in GaN epitaxial layers grown on silicon (111) substrates by metalorganic vapor phase epitaxy has been investigated. The insertion of AlN/GaN superlattices was found to decrease the stress sufficiently for avoiding crack formation in an overgrown thick GaN layer. X-ray diffraction and photoluminescencemeasurements are used to determine the effect of these AlN/GaN superlattices on the strain in the subsequent GaN layers. A reduction of threading dislocation density is also observed by transmission electron microscopy and atomic force microscopy when such superlattices are used. Strong band edge photoluminescence of GaN on Si(111) was observed with a full width at half maximum of the bound exciton line as low as 6 meV at 10 K. The 500 arcsec linewidth on the (002) x-ray rocking curve also attests the high crystalline quality of GaN on Si (111), when using these AlN/GaN superlattices.

Al-induced crystallization of co sputtered hydrogenated amorphousgermaniumfilms,deposited at 220 °C, onto crystalline silicon substrates is investigated by Raman and infrared spectroscopies as a function of the Al concentration Aluminum induces partial crystallization of the films for metal concentrations smaller than ∼1.3 at. %. A sort of explosive crystallization of the films occurs within a narrow Al concentration range Raman spectra do not display any crystallization signal for metal concentrations above this narrow range. Data of the extended x-ray absorption fine structure of the coordination and of the local order around gallium, in Ga-doped are used to propose an overall picture of the microscopic mechanisms behind these results. A comparative analysis suggests that the crystallization seeds are fourfold-coordinated Al atoms sitting at the center of perfect tetrahedral Ge sites.

Electromigration tests at temperatures between 340 and and current densities between 1.0 and have been performed to determine the temperature dependence of the critical length effect in 0.5-μm-wide Cu/oxide dual-damascene interconnects with 0.1 μm silicon nitridepassivation. A focused-ion-beam-induced contrast imaging technique is used to locate failure sites of critical length test structures.Statistical analysis [E. T. Ogawa et al., Appl. Phys. Lett. 78, 18 (2001)] yields a threshold-length product of 3700 A/cm, and a temperature dependence is not observed within the temperature range

A systematic study of the nature of arsenic incorporation in GaN grown by molecular-beam epitaxy is presented. The samples were grown with concentrations of arsenic ranging from to Secondary ion mass spectroscopy data show that increasing the As concentration has the effect of increasing the amount of As in the nitrogen site as compared to As in the gallium site. This trend is used to explain the reduction in carrier mobility with increasing As concentration.

The initial growth process of thin films on Si(001) surfaces is examined by scanning tunneling microscopy. The surface morphology of the film critically depends on the C fraction in the film. Evidence is presented on an atomic scale that the epitaxialgrowth of films with large C fractions is dominated by phase separation between Si–C and Si–Ge, concomitant with C condensation on the surface of the growingfilms. We find that the addition of a thin (1–2 ML) SiGe interlayer between the film and the Si substrate drastically improves the filmstructure, leading to a planar morphology even with large C fractions present in the film.

alloys with x up to 0.7 were grown by metalorganic chemical vapor deposition and their optical properties were investigated by deep UVtime-resolvedphotoluminescence(PL)spectroscopy. Our results revealed that both the activation energy of the PL emission intensity and the PL decay lifetime exhibit sharp increases at x of around 0.4. The results can be understood in terms of the sharp increase of the impurity binding energy or the carrier/exciton localization energy around A three orders of magnitude increase in resistivity of undoped AlGaN alloys at x of around 0.4 was also observed, which further corroborated the optical results.

We have demonstrated sub-100 ps jitter operation of a pressurized high-voltage air spark gap triggered by a femtosecond Ti:Sapphire laser. Time delay statistical fluctuations with a standard deviation as low as were obtained.

In the Stranski–Krastanov system, the lattice mismatch between the film and the substrate causes the film to break into islands. During annealing, both surface energy, and elastic energy drive the islands to coarsen: some islands enlarge and others shrink, keeping the total island volume constant. The islands produced this way are usually uneven in size and spacing. Motivated by several related studies, we suggest that stable, uniform islands should form when a stiff ceiling is placed at a small gap above the film. After contacting the ceiling, the islands are constrained to grow laterally and remain coherent with the substrate, preventing further stress relaxation. In fact, we show that the role of elasticity is reversed: with the ceiling, the total elastic energy stored in the system increases as the islands coarsen laterally. On the other hand, the total surface energy decreases as the islands coarsen. Consequently, the islands select an equilibrium size to minimize the combined elastic energy and surface energy. We estimate the equilibrium island size by analyzing an idealized model.

The effect of crystal polarity on the electrical properties of Ti/Al contacts to substrate has been investigated. The Ti/Al contacts prepared on Ga-face substrate became ohmic with a contact resistivity of after annealing at temperatures higher than 600 °C for 30 s. On the contrary, the contacts on N-face substrate exhibited nonlinear current–voltage curve and high Schottky barrier heights over 1 eV were measured at the same annealing conditions. These results could be explained by opposite piezoelectric-field at GaN/AlN heterostructure resulted from different polarity of the GaN substrate.

The bias-enhanced nucleation (BEN) of diamonds on a Si substrate, using a mask and microwaveplasma-enhanced chemical vapor deposition (MPE-CVD), was examined. Experimental results indicate that the electron-emission-enhanced nucleation mechanism proposed herein governs the nucleation of diamonds on the partially patterned substrate. The variation of nucleation density on the partially patterned substrate also reveals that the BEN of diamonds in the MPE-CVD process follows the proposed mechanism.

Copper and parylene-n are studied for ultralarge scale integration circuits because of their low electrical resistivity,resistance to electromigration and low dielectric constant, chemical inertness, and compatibility with currentintegrated circuit manufacturing, respectively. Copperdiffusion observed at and above 300 °C in correlates to an increase in the crystallinity of the α phase and subsequent transformation to the more open structure of β parylene. Titanium nitride (oxygen) [TiN(O)]/titanium (Ti) bilayers are successfully implemented as a diffusion barrier. TiN is proven to be a very good diffusion barrier up to 500 °C for copper due to its large negative heat of formation and hence its thermal stability. Incorporation of an intermediate titanium layer reduced the residual stress and thermal mismatch between and TiN. Without the Ti layer thermal cracking of TiN occurred. The presence of the buffer layer had no detrimental effects on the overall resistivity. The effectiveness of the barrier is attributed to stuffing of the grain boundaries with oxygen and nitrogen. This results in the elimination of rapid diffusion paths. This work provides the foundation for future implementation of for higher temperature microelectronics.

Arsenic doping at concentrations during Si(001) growth from hydride precursors gives rise to strong As surface segregation, low film growth rates poor electrical activation, and surface roughening. Based upon the results of temperature-programmed desorption studies of Si(001):As surface processes during film deposition, we have investigated the use of temperature-modulated growth including periodic arsenic desorption (10 s at 1000 °C) from the surface segregated layer. Both constant-temperature and temperature-modulated Si(001):As layers were grown at selected as a compromise between maximizing and providing a usable deposition rate, by gas-source molecular beam epitaxy from mixtures. For constant-temperature growth, is only 0.08 μm h−1, the fraction of electrically active dopant is 55%, and filmsurfaces are very rough (rms roughness In sharp contrast, -modulated layers exhibit increases in by 2.5× to 0.20 μm h−1, 100% electrical activity, and atomically smooth surfaces with The results are explained based upon the competition among As surface segregation,desorption, and incorporation rates.

We utilize very sensitive magnetic resonance measurements to observe changes in the densities of interface trap centers hundreds of hours after irradiation. Our observations provide direct atomic-scale evidence for slow changes in interface-state density distributions which appear after the devices have been damaged. Our observations also explain (at least in part) why different groups report somewhat different shapes for the density of interface states in the siliconband gap.

The electrical properties of thick amorphouscarbonfilms with sequential layered structure, grown by magnetron sputtering on Si substrates at room temperature, were investigated. At low electric fields, the conduction is due to the variable range hopping mechanism. At high electric fields, thermally assisted band-to-band indirect tunneling is the dominant conduction mechanism, while the Arrhenius plots of the current show a deviation from straight lines in the form of continuous bending satisfying the Meyer–Nelder rule. Comparative studies of low-frequency noise in single layer and layered films indicate that the noise in the layered originates from traps located mainly at the interfaces of the bilayers.

We measured the recombination lifetime of degenerate for three different compositions that correspond to 0.66, and 0.78 (band gaps of 0.74, 0.60, and 0.50 eV, respectively) over the doping range of The Auger recombination rate increases slowly with decreasing band gap, and it matches the behavior predicted for phonon-assisted recombination.